During a hypothetical severe accident, most of the iodine entering the containment would be in particulate form that would undergo transport and deposition phenomena of aerosols. After a certain period of time, a large fraction of this aerosol would be deposited in the containment sump, either by settling or by diffusiophoresis. Dissolution of iodine compounds would result in the formation of involatile aqueous iodide ions. Under radiation, the aqueous iodide in the sump is a potential source of volatile iodine compounds.
Radiolytic oxidation of the iodide ions in the containment sump to produce molecular iodine (I2) was considered as a major issue in the PIRT of the EURSAFE project and it is being investigated within the Source Term area (WP16) of the SARNET project. There are two major reasons for this. Firstly, I2 is a highly volatile compound, which is much more difficult to trap by physical methods than aerosols. Secondly, it can act as a precursor for organic iodide compounds, which may be even more volatile than I2.
This paper presents a review of the modelling fundamentals currently implemented in the main iodine chemistry codes underlying reactor accident predictions (IMPAIR3, INSPECT, IODE from ASTEC, MAAP). Some tests from the available database (AEAT tests, University of Toronto tests and others) have been simulated with those tools and the remaining uncertainties are assessed by comparison of the predictions with the data. In addition, a discussion based on a specific comparison between the two existing models in ASTEC resulted in a recommendation concerning their adequacy. Finally, short-term experimental plans to extend the database with experiments from the EPICUR programme (carried out by IRSN) are summarised.